U.S. patent number 6,292,556 [Application Number 08/965,630] was granted by the patent office on 2001-09-18 for local loop telecommunication repeater housings employing thermal collection, transfer and distribution via solid thermal conduction.
This patent grant is currently assigned to Anacapa Technology, Inc.. Invention is credited to Erich K. Laetsch.
United States Patent |
6,292,556 |
Laetsch |
September 18, 2001 |
**Please see images for:
( Certificate of Correction ) ** |
Local loop telecommunication repeater housings employing thermal
collection, transfer and distribution via solid thermal
conduction
Abstract
An improved thermal design for passively cooled
telecommunication repeater housings for use with wire transmission
in the local loop outside plant is achieved by replacing the known
convection based heat transfer designs with a design based on solid
thermal conduction. A thermal chassis includes thermal collection,
transfer and distribution members that collect the repeater
modules' waste heat through respective thermal interfaces, transfer
the waste heat along respective thermal conduction paths to the
environmental enclosure, and then distribute the waste heat over a
substantial portion of the enclosure's available surface area to
form an enlarged thermal interface for convectively transferring
the waste heat to the ambient air. Heat transfer is further
improved by expanding the enclosure's external surface area and
fabricating the distribution members so that they are in permanent
and intimate thermal contact with the enclosure's expanded surface
area.
Inventors: |
Laetsch; Erich K. (Reno,
NV) |
Assignee: |
Anacapa Technology, Inc. (Reno,
NV)
|
Family
ID: |
25510242 |
Appl.
No.: |
08/965,630 |
Filed: |
November 6, 1997 |
Current U.S.
Class: |
379/338;
361/690 |
Current CPC
Class: |
H05K
7/20445 (20130101) |
Current International
Class: |
H05K
7/20 (20060101); H05K 007/20 () |
Field of
Search: |
;379/338,348
;361/722,690,715 ;340/425.2,425.1 ;174/7S |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Bell System Practices (AT&T Co), 809-Type, Repeater Cases.
Description Installation, Splicing, and Maintenance, Section
640-525-30. Issue 2, Sep. 1980, Bell System. .
Supplemental Information Disclosure Statement. .
Second Supplemental Information Disclosure Statement. .
Third Supplemental Information Disclosure Statement. .
AT & T Technologies, 1984 Product Guide, AT&T 640-525-212,
Issue 4, Feb. 1985, pp. 1-37, 475G2, 475J, and 475K Apparatus
Cases. .
AT & T Technologies, 1986, 1986 Product Guide, AT&T
Practice Standard, AT&T 640-527-107, Issue 3, Mar. 1986 pp.
1-47, 479-Type Apparatus Case. .
SPC Specialty Product Company, Product Sheet, 1996..
|
Primary Examiner: Isen; Forester W.
Assistant Examiner: Storm; Donald L.
Attorney, Agent or Firm: McAndrews, Held & Malloy,
Ltd.
Claims
What is claimed is:
1. A passively cooled repeater housing for a plurality of repeater
modules for use in the outside plant of the local loop of a
telecommunication transmission network, said repeater housing
providing plug-in access to the repeater modules, said repeater
housing comprising:
an environmental enclosure having a removable cover and at least
one sidewall;
a thermal collection member disposed within said environmental
enclosure and adapted to form a thermal interface with at least one
of said repeater modules and to collect waste heat generated by at
least one of said repeater modules;
a thermal distribution member in thermal contact with said at least
one sidewall and adapted to distribute the waste heat over said at
least one sidewall; and
a thermal transfer member adapted to provide thermal conduction
from said thermal collection member to said thermal distribution
member;
wherein said thermal distribution member remains in thermal contact
with said at least one sidewall upon removal of said cover.
2. The repeater housing of claim 1, wherein said thermal collection
member is adapted to accommodate standard sized repeater
modules.
3. The repeater housing of claim 1, wherein said repeater housing
further includes at least one slot disposed within said
environmental enclosure for removably accommodating at least one
voltage surge protector assembly, said slot having an open end at
or about the top of said environmental enclosure, whereby said at
least one voltage surge protector assembly is removable
independently of the repeater modules.
4. The repeater housing of claim 1, wherein said thermal collection
member is in thermal contact with a major proportion of the surface
area of at least one of said plurality of repeater modules.
5. The repeater housing of claim 1, wherein said thermal collection
member forms said thermal interface with at least one repeater
module over less than the full surface of the repeater module.
6. The repeater housing of claim 1, wherein said thermal collection
member is adapted to accommodate differently sized repeater
modules.
7. The repeater housing of claim 1, further comprising at least one
shim disposed between the thermal collection member and at least
one of said plurality of repeater modules.
8. The repeater housing of claim 1, wherein said thermal
distribution member and an interior surface of said at least one
sidewall are formed in complementary configurations, thereby
facilitating conduction of waste heat from said thermal
distribution member to said at least one sidewall.
9. The repeater housing of claim 1, further comprising a layer of
thermally-conductive adhesive between said thermal distribution
member and said at least one sidewall.
10. The repeater housing of claim 1, wherein said thermal
distribution member is located on the exterior of the environmental
enclosure.
11. The repeater housing of claim 1, wherein two or more of said
thermal collection member, said thermal transfer member, and said
thermal distribution member are integrally formed into a single
unit.
12. The repeater housing of claim 11, wherein said single unit
comprises a sleeve adapted to accommodate one or more repeater
modules.
13. The repeater housing of claim 12, further comprising a
plurality of sleeves adapted to accommodate one or more repeater
modules.
14. The repeater housing of claim 13, wherein each of said sleeves
is in thermal contact with at least one other of said sleeves,
whereby waste heat is transferred from a hotter area to a cooler
area.
15. The repeater housing of claim 1, wherein the environmental
enclosure is a cylindrical enclosure.
16. The repeater housing of claim 1, wherein the environmental
enclosure is a rectangular enclosure.
17. The repeater housing of claim 1, wherein the environmental
enclosure is formed from a material selected from the group
consisting of stainless steel and aluminum.
18. The repeater housing of claim 1, wherein the environmental
enclosure is formed from a material selected from the group
consisting of fiberglass and plastic.
19. The repeater housing of claim 1, wherein said at least one
sidewall is formed of a moldable material, and said at least one
sidewall is formed over said thermal distribution member.
20. The repeater housing of claim 1, wherein said thermal contact
between said thermal distribution member and said at least one
sidewall is provided by a compression fit.
21. The repeater housing of claim 1, wherein said environmental
enclosure comprises a plurality of exteriorly formed fins.
22. The repeater housing of claim 1, wherein said thermal
distribution member comprises a plurality of fins and said
environmental enclosure comprises a corrugated surface adapted to
engage said plurality of fins, thereby forming a plurality of
thermal contacts between said surface and said fins.
23. The repeater housing of claim 1, wherein said thermal
distribution member comprises a plurality of fins and said
environmental enclosure comprises a convoluted surface adapted to
engage said plurality of fins, thereby forming a plurality of
thermal contacts between said surface and said fins.
24. The repeater housing of claim 1, further comprising a solar
shield assembly attached to the exterior of the environmental
enclosure.
25. The repeater housing of claim 24, wherein said solar shield
assembly comprises a solar shield and fins, and said solar shield
is attached to said fins and said fins are attached to the exterior
of the environmental enclosure.
26. A passively cooled repeater housing for a plurality of repeater
modules for use in the outside plant of the local loop of a
telecommunication transmission network, said repeater housing
providing plug-in access to the repeater modules, said repeater
housing comprising:
an environmental enclosure having a removable cover and at least
one sidewall; and
a thermal chassis disposed within said environmental enclosure and
in thermal contact with said at least one sidewall, said thermal
chassis being adapted to removably accommodate said plurality of
repeater modules, to collect waste heat generated by said plurality
of repeater modules, and to conduct waste heat to said at least one
sidewall;
wherein said thermal chassis remains in thermal contact with said
at least one sidewall upon removal of said cover.
27. The repeater housing of claim 26, wherein said thermal chassis
is adapted to accommodate standard sized repeater modules.
28. The repeater housing of claim 26, wherein said thermal chassis
further includes at least one slot for removably accommodating at
least one voltage surge protector assembly, said slot having an
open end at or about the top of said thermal chassis and providing
plug-in access to said voltage surge protector assembly, whereby
said voltage surge protector assembly is removable independently of
the repeater modules.
29. The repeater housing of claim 26, wherein said thermal chassis
is in thermal contact with a major proportion of the surface area
of at least one repeater module.
30. The repeater housing of claim 26, wherein said thermal chassis
is in thermal contact with at least one repeater module over less
than the full surface of the repeater module.
31. The repeater housing of claim 26, wherein said thermal chassis
adapted to accommodate a plurality of differently sized repeater
modules.
32. The repeater housing of claim 26, further comprising at least
one shim for improving said thermal contact between said thermal
chassis and at least one of said plurality of repeater modules.
33. The repeater housing of claim 26, wherein said thermal chassis
and an interior surface of said at least one sidewall are formed in
complementary configurations, thereby facilitating conduction of
waste heat from said thermal chassis to said at least one
sidewall.
34. The repeater housing of claim 26, further comprising a layer of
a thermally-conductive adhesive between said thermal chassis and
said at least one sidewall.
35. The repeater housing of claim 26, wherein the environmental
enclosure is a cylindrical enclosure.
36. The repeater housing of claim 26, wherein the environmental
enclosure is a rectangular enclosure.
37. The repeater housing of claim 26, wherein the environmental
enclosure is formed from a material selected from the group
consisting of stainless steel and aluminum.
38. The repeater housing of claim 26, wherein the environmental
enclosure is formed from a material selected from the group
consisting of fiberglass and plastic.
39. The repeater housing of claim 26, wherein said environmental
enclosure comprises a shell that defines said at least one
sidewall, and said shell is formed over said thermal chassis.
40. The repeater housing of claim 26, wherein said thermal contact
between said at least one sidewall and said thermal chassis is
provided by a compression fit.
41. The repeater housing of claim 26, wherein said environmental
enclosure is fixed to said thermal chassis.
42. The repeater housing of claim 26, wherein said thermal chassis
is removable from said enclosure.
43. The repeater housing of claim 26, wherein said environmental
enclosure comprises a plurality of exteriorly formed fins.
44. The repeater housing of claim 26, wherein said thermal chassis
comprises a plurality fins and wherein said environmental enclosure
comprises a corrugated surface adapted to form a plurality of
thermal contacts between said surface and said fins.
45. The repeater housing of claim 26, wherein said thermal chassis
comprises a plurality fins and wherein said environmental enclosure
comprises a convoluted surface adapted to form a plurality of
thermal contacts between said surface and said fins.
46. The repeater housing of claim 26, further comprising a solar
shield assembly attached to the exterior of the environmental
enclosure.
47. The repeater housing of claim 46, wherein said solar shield
assembly comprises a solar shield and fins, and said solar shield
is attached to said fins and said fins are attached to the exterior
of the environmental enclosure.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to passively cooled repeater housings for
use in a telecommunication network's wire transmission local loop
outside plant and more specifically to repeater housings having
improved thermal transfer characteristics, improved performance
under solar loads and direct access to repeaters and voltage surge
protectors.
2. Description of the Related Art
In the telecommunications industry, voice, data and video
transmission signals are transmitted over wire, fiber optic and
wireless networks. Although the fiber optic and wireless networks
were designed to meet the current demand for high speed signal
transmission, the massive investment in the wire network, or the
"copper plant" as it is commonly referred to, necessitates its
continued use. The cost and time involved to completely replace the
millions, if not billions, of miles of copper (or aluminum) wires
in the United States alone with fiber optic lines and wireless
networks is prohibitive. Although originally designed to carry only
voice grade signals, the continued development of increasingly
sophisticated digital signal processing (DSP) techniques such as
T-carrier, ISDN, Direct Digital Service (DDS) and most recently,
High bit-rate Digital Subscriber Line (HDSL) allow the
telecommunications industry to transmit rapidly growing volumes of
high speed signals over the copper plant in a more cost effective
manner than conversion to the newer transmission technologies in
all but the high volume networks.
As shown in FIG. 1, a typical telecom network 10 includes a number
of central offices 12 that transmit a massive amount of very high
speed signals between offices over inter-office trunks 14 and a
number of local loops 16 that distribute portions of the signals
from a central office 12 to a customer premises 18 and between
customer premises 18. A clear distinction has existed between the
offices' inter-office trunks 14 and the local loops 16. First, each
central office will typically service many user premises. As a
result, the cost of replacing the copper plant for the central
offices' inter-office trunks is much lower than replacing it for
all the individual users. Second, the signal traffic between
central offices is typically much higher volume and much higher
speed than is required in the local loop.
As a result, inter-office trunks 14 have been largely converted
from copper wire to the more sophisticated fiber optics, microwave
transmission and even satellite transmission systems while the
local loops have used the updated DSP technologies in conjunction
with the existing and even new installation copper 20. However, for
the last several years, the explosive growth in demand for high
speed telecommunications services such as those required for
business networking and the Internet has been stressing the
capabilities of the copper network in the local loop.
One particular area in which the copper network is being stressed
occurs in the "outside plant", i.e. that part of the local loop
that lies outside the controlled environments of telecom or user
buildings, generally regarded as the lowest technology link in the
network and symbolized by the lineman on a pole or in a
manhole.
As signals are transmitted over the copper wires in the outside
plant they degrade and lose signal integrity. As a result, the
industry has developed circuits called "mid-span repeaters" or
simply "repeaters" that regenerate a degraded signal. Depending
upon the transmission technology used, the repeaters are placed
every three to twelve thousand feet along the transmission
path.
Repeaters are manufactured by numerous suppliers to support a
variety of copper transmission technologies. Several industry
standard connector and case standards are followed to allow
repeaters from different suppliers and of different technologies to
be interchanged. FIGS. 2a and 2b illustrate a standard 239
mini-repeater 22 often used with older T-1 technology and a
standard 239 double-wide repeater 24 that is commonly used with the
ISDN, DDS and HDSL technologies. The T-1 239 mini-repeater
generates approximately 0.75 watts of waste heat whereas an HDSL
239 double-wide, while only twice as big, generates up to 6 watts
of waste heat. Because of the nearly order of magnitude increase in
power consumption, the 239 double-wide is frequently provided with
slits that facilitate air flow over the hot parts to convectively
remove heat. The power consumption of ISDN and DDS repeaters is
also substantially greater than T-1 239 mini-repeaters, but less
than that of the more sophisticated HDSL repeaters.
Because mid-span repeaters are used in the outside plant,
frequently in manholes 28, they must be placed in a repeater
housing 26 such as the AT&T '809 Apparatus Case 30 shown in
FIGS. 3a and 3b, the SPC Series 7000 Enclosure 32 shown in FIGS. 3c
and 3d, or the generic cabinet style enclosure 34 shown in FIG. 3e.
The primary function of these known repeater housings is to provide
an environmental enclosure that shields the repeaters from the
elements; wind, rain, dust, solar energy, animals, vandals etc.
They are oftentimes formed from strong corrosion resistant
materials such as stainless steel or hard plastic and are
hermetically sealed, often under a positive pressure. In mild
environments the repeater housing do not have be corrosion
resistant and above ground cases are often vented.
The housings must accommodate standard sized repeater modules that
are built by a number of vendors. The housings must also provide
physical access to repeater modules and voltage surge protectors so
that they can be removed and replaced in the field in a "plug-in"
manner without having to disassemble the module or disturb the
operation of other repeaters. Furthermore, to improve reliability
and avoid the expense of requiring electrical power at each
repeater site, the housing must be passively cooled to remove the
waste heat generated by the repeaters. It is well understood in the
telecommunications industry that thermal stress can cause short
term failures, intermittent operation deviations and significantly
shorten the life of electronic equipment. Most telecom electronics
is installed in buildings that provide a controlled and relatively
benign thermal environment. In contrast, repeaters deployed in the
outside plant must work in the harsh, natural environment.
The AT&T '809 apparatus case 30 shown in detail in FIG. 4 and
the double size '819 apparatus case described in AT&T Practice
640-525-307 Issue 5, April 1986 is a molded plastic rectangular
housing that is lightweight, does not corrode, and optimizes the
use of available space. The '819 obsoleted AT&T's earlier '479
apparatus case described in AT&T Practice 640-527-107 Issue 3,
March 1986 that had the same general shape but was constructed from
cast iron, and thus extremely heavy and subject to corrosion.
The '809 includes a molded base 36 for receiving a stub cable 38
from a splice case in the local loop and a mounting bracket 40 for
mount the case on the wall of a manhole, for example. Pressure and
pressure relief valves are also provided in the base. Stub cable 38
is split into individual wires that are run through base 36 and
wire-wrapped to the backside of repeater/protector connectors 42,
which have a female PCB edge connector 44 for mounting the repeater
module and multiple sockets 46 for mounting gas tube style voltage
surge protectors 48.
A molded housing 50 having an array of plastic stubs 52 is bolted
on base 36 so that stubs 52 define slots 54 over the respective
repeater/protector connectors 42 for separating and supporting the
repeater modules. A molded cover 56 is then bolted on top of
housing 50. The cover can be removed to gain direct access to the
top of the enclosed repeater modules for easy installation and
replacement. The illustrated '809 case is designed, physically and
electrically, to hold 12 239 mini-repeater modules 22 or 6
non-standard repeater modules 25 with 2 slots used for support
functions. The '809 case was designed for the 239 mini-repeater and
thus does not physically accommodate the standard 239 double-wide
case. Some suppliers have developed a variation of the 239
double-wide that is even wider and has slots 58 in the case to
allow it to fit into two slots in the '809 and '819.
To make the best use of the space available inside housing 50,
voltage surge protectors 48 are positioned in connector sockets
underneath the repeater modules. To gain access to the protectors,
a lineman must first remove the repeater module, taking it out of
service temporarily. Because the voltage surge protectors are
positioned at the bottom of narrow slots 54 they can be very
difficult to remove. Consequently, AT&T provides a special 829A
tool and a detailed multi-step process for extracting the gas
protectors. In practice, lineman sometimes use a long screwdriver
to pop the protectors loose. However, with +/-130 volts active on
the contacts of the protector sockets, attempted service without
the proper tool can be hazardous, both to the lineman and to the
equipment.
Although the practice makes no mention of thermal considerations,
the '809 relies on convection and, to a lesser degree, radiation to
remove waste heat from the repeater modules. The repeater module
and, in the case of the slit, modified double-wide, the components
themselves heat the air which transfers some heat to the adjacent
walls of the case and rises to convectively transfer the rest of
the heat to the top of the case. The walls and end of the case
absorb the waste heat and then convectively transfer it to the
surrounding environment. Notice, stubs 52 position, but do not
tightly enclose the repeater modules to encourage air flow to
improve convective heat transfer to the top of the case.
The SPC 7000 Series enclosure 32 shown in FIGS. 5 and 6 is a
thin-walled stainless steel cylindrical enclosure. The 7000 Series
enclosure includes a cylindrical base 60 into which it receives a
stub cable 62. A lightweight thin aluminum basket 64 is centrally
mounted on a bracket 66 in base 60. A number of female PCB repeater
connectors 68 are mounted in slots in the bottom of the basket with
their pins 70 wire wrapped (not shown) to the stub cable. A voltage
surge protector assembly 72 is then mounted on the back side of
connector 68 and repeater modules 24 are mounted on the top side in
the basket. Bracket 66 allows basket 64 to be tipped to access the
backside wiring. Alternately, the basket can be replaced with a
chassis in which the modules are inserted horizontally from one
side and access to the protectors is gained from the other side. A
dome 74 fits over base 60 and is hermetically sealed using a
V-groove clamp 76, an O-ring 78a and an O-ring retainer 78b.
Similar to the '819, the Series 7000 enclosure relies on radiation
and convection to move the waste heat generated by the repeater
modules to the dome and then to the surrounding environment. To
this end, the 239 double-wide repeater modules and the basket are
formed with slits to encourage air flow. In its normal upright
position, the heated air rises to the top of the dome where it is
then convectively transferred to the environment.
Access to the repeater is gained by removing the entire cylindrical
dome. The removal of the entire cylindrical dome of an SPC 7000
style repeater housing is of little consequence in above ground and
low density below ground (manhole) installations, however, with
sharply increased crowding in below ground facilities, the extra
clearance required to remove the entire dome has become a drawback
to the otherwise satisfactory cylindrical dome repeater housing
configuration. In response, repeater housing mounting brackets have
been developed that allow the entire housing to pivot away from the
mounting surface sufficiently to permit the cylindrical dome to be
removed without requiring excessive vertical clearance directly
above its installation.
While such access to the modules and voltage protectors may seem
convenient, in the reality of a crowded manhole, "tilt, swivel and
around the back" represent difficult access, excessive installation
and service time and risk to the hundreds of wires connected to the
repeater modules. Furthermore, the +/-130 VDC span power is not
deactivated during service of the repeater housing, therefore,
installation and removal of the voltage protector assemblies
connected to this voltage must be performed with serious
caution.
The '819 apparatus case and Series 7000 enclosure, and the thermal
transfer techniques they embody, are designed to handle up to 25
239 mini-repeaters and do so with no problem. However, those same
housings are limited to 2 or maybe 3 HDSL repeaters before their
thermal transfer capabilities are overloaded. With the demand for
high bandwidth service continuing to grow and the amount of
available space either below ground in manholes or above ground
reaching or exceeding capacity, repeater housings in which a
majority of the slots must remain empty for thermal reasons is
clearly a problem. Furthermore, direct, easy and safe access to the
repeater modules and their voltage surge protectors is an important
consideration.
SUMMARY OF THE INVENTION
In view of the above problems, the present invention provides an
improved thermal design based upon solid thermal conduction for
passively cooled repeater housings used in a telecommunication
network's wire transmission local loop outside plant.
This is accomplished by using thermal collection, transfer and
distribution members to collect the repeater modules' waste heat
through respective thermal interfaces, transfer the waste heat
along respective thermal conduction paths to the environmental
enclosure, and then distribute the waste heat over a substantial
portion of the enclosure's available surface area to form an
enlarged thermal interface for convectively transferring the waste
heat to the ambient air. In a currently preferred approach, the
collection, transfer and distribution functions are integrated in a
thermal sleeve that minimizes the thermal resistance between the
module and the enclosure. To further improve heat transfer, the
distribution member and enclosure are preferably formed to
distribute the waste heat over an expanded external surface area.
This is accomplished by designing the repeater and voltage
protector assemblies so that they can be removed via top/front
access, preferably independently of each other. This allows the
distribution members to be fabricated in permanent and intimate
thermal contact with the enclosure by, for example, compression
fitting complementary corrugation pieces or molding one inside the
other.
These and other features and advantages of the invention will be
apparent to those skilled in the art from the following detailed
description of preferred embodiments, taken together with the
accompanying drawings, in which:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1, as described above, is a simplified illustration of a
telecommunications network;
FIGS. 2a and 2b, as described above, depict a standard 239-mini
repeater and a standard 239 double-wide repeater case,
respectively;
FIGS. 3a through 3e, as described above, depict a variety of known
repeater housings;
FIG. 4, as described above, is a perspective and partially cut-away
view of an AT&T '809 apparatus case;
FIG. 5, as described above, is an exploded view of an SPC 7000
series repeater housing;
FIG. 6, as described above, is a tipped view of the SPC 7000 series
repeater housing;
FIG. 7 is a thermal resistance model of a repeater housing;
FIGS. 8a through 8e are simplified illustrations of thermal
collection, transfer and distribution mechanisms in a thin-walled
environmental enclosure in accordance with the present
invention;
FIG. 9 is a simplified thermal resistance model of a repeater
housing incorporating the thermal collection, transfer and
distribution mechanisms;
FIG. 10 illustrates a preferred thermal sleeve for performing the
thermal collection, transfer and distribution;
FIGS. 11a through 11d illustrate different embodiments of a voltage
surge protector assembly for the repeater that facilitate direct
access within the repeater housing;
FIG. 12 is a perspective and partially enlarged view of a repeater
housing that uses the thermal sleeve within a modified SPC 7000
series thin-walled environmental enclosure;
FIG. 13 is an exploded view of the thermal sleeve and the actuator
mechanism for urging the sleeve against the interior wall of the
environmental enclosure of the repeater housing shown in FIG.
12;
FIG. 14 is a plan view of the repeater housing shown in FIG. 12 in
its expanded and retracted positions;
FIGS. 15a and 15b are views along section line 15--15 in FIG. 14 of
the repeater housing in its expanded and retracted positions,
respectively;
FIG. 16 is a tipped view of the repeater housing shown in FIG.
12;
FIG. 17 is a perspective and partially enlarged view of a solar
shield for the repeater housing shown in FIG. 12;
FIGS. 18a, 18b and 18c are respectively detailed implementations of
the fins shown in FIG. 17;
FIG. 19 is an exploded view of a preferred above-ground cylindrical
repeater housing;
FIG. 20 is a partially cut-away view of the assembled cylindrical
repeater housing shown in FIG. 19;
FIG. 21 is an exploded view of a preferred below-ground cylindrical
repeater housing;
FIGS. 22a and 22b are respectively plan views of the below-ground
repeater housing without its cover and the bottom side of the
cover;
FIGS. 23a and 23b are partial sectional views showing the
below-ground cylindrical repeater housing in its uncovered and
covered configurations, respectively; and
FIG. 24 is an exploded view of a threaded fin below-ground
cylindrical repeater housing.
DETAILED DESCRIPTION OF THE INVENTION
The present invention applies thermal modeling and design
principles to first identify and then solve the thermal transfer
problems in known local loop repeater housings. As the very
simplified thermal model 100 for the known repeater housings shown
in FIG. 7 illustrates, waste heat generated by the aggregation of
"HOT PARTS" in the repeater modules flows to the cooler AMBIENT
AIR. With the repeaters operating, the temperature of the heat
generating parts (HOT PARTS) and all other thermal nodes between
the HOT PARTS and the AMBIENT AIR surrounding the repeater housing
will increase until thermal equilibrium is reached, i.e. the
quantity of heat flowing out of the repeater housing equals the
quantity of waste heat generated within. The thermal resistances
represent the main heat transfer paths associated with solid and
gaseous conduction, natural convection and radiation, and take into
consideration the thermal properties of thin materials and poorly
mated surfaces. In contrast to simple electrical networks with
similar schematic appearance, most thermal resistances vary
non-linearly with the temperature across and the heat flow through
them. Accordingly, a precise analysis of this heat flow system
would involve sophisticated techniques such as Finite Element
Analysis and/or Computation Fluid Dynamics to solve the array of
partial differential equations.
Heat generated in the aggregation of HOT PARTS can flow outward
along three main paths. The primary path .THETA..sub.H-E relies
upon natural convection to circulate air through the holes in the
repeater modules and carry the heat to the inner surface of the
ENCLOSURE at its highest point. Another convective path
.THETA..sub.H-C transfers a portion of the waste heat to the
CHASSIS (the Series 7000 basket and '819 stubs). The last major
path .THETA..sub.H-M uses a combination, which depends upon the
specific packaging of the repeater, of solid and gaseous
conduction, natural convection and radiation to transfer waste heat
to the MODULE casing.
Heat transferred to the repeater MODULE casing can flow outward
along two main paths. A first path .THETA..sup.M-E to the inner
surface of the ENCLOSURE is almost entirely via natural convection
and is very dependent upon the design of the CHASSIS. The small
space generally provided between MODULE and CHASSIS can severely
restrict natural convection air flow over the sides of the MODULE
because of boundary layer effects. The other path .THETA..sup.M-C
to the CHASSIS uses convection, gaseous conduction and radiation,
and is also very dependent upon the CHASSIS design. The
contribution of solid conduction is minimal because the mating
surfaces are not sufficiently conforming and under enough contact
pressure to exclude the air interface. Furthermore, the profusion
of holes in both the repeater MODULE and in the CHASSIS
significantly reduce the surface area available for MODULE to
CHASSIS contact.
The path .THETA..sub.C-E from the CHASSIS to the ENCLOSURE includes
natural convection, which concentrates the transferred heat on the
inner top surface of the ENCLOSURE, radiation, which transfers a
small fraction of the waste heat to the side walls, and solid
conduction to the bottom of the ENCLOSURE. The thin metal or
plastic CHASSIS and the frequent presence of thermal barriers in
the form of mechanical joints generally minimize heat transfer
along the solid conduction path.
The final path .THETA..sub.E-A is from the inner surface of the
ENCLOSURE to the surrounding AMBIENT AIR where the waste heat is
dissipated. That part of the path from the inner surface to the
outer surface of the ENCLOSURE is via solid conduction. Because the
inner to outer distance is small and the transfer area large, the
solid conduction resistance through to the outside of the ENCLOSURE
is negligible. However, even if the environmental ENCLOSURE is
metallic as in the stainless steel SPC 7000, the thermal resistance
representing the diffusion of waste heat across the surface area of
the thin metal or most plastic ENCLOSURES is very high and thus the
heat transferred to an area on the ENCLOSURE remains localized.
From the heated surface of the ENCLOSURE, the waste heat is then
transferred via natural convection to the surrounding AMBIENT
AIR.
This model shows that known repeater housings 1) primarily use high
thermal resistance, natural convection within the housing to
transfer waste heat to the environmental enclosure and 2) make
inefficient use of the surface area of the enclosure as a thermal
interface to the surrounding ambient air. As a result the capacity
of the known repeater housings to dissipate heat and thus the
number of HDSL and other high or medium power consumption repeaters
(such as ISDN and DDS) that can be deployed within known housings
is severely constrained. To solve this problem, Applicant applies
the principles of thermal collection, transfer, and distribution
via solid thermal conduction as illustrated in FIGS. 8a through 8e
to reduce the thermal resistance between the HOT PARTS and the
AMBIENT AIR with the result being a dramatic increase in the
thermal transfer capacity of the repeater housing.
Thermal collection members 102 shown in FIG. 8a and 104 shown in
FIGS. 8b-8e, which are manufactured from a thermally conductive
material such as aluminum or thermally conductive plastic, form a
thermal interface 106 with repeater module 108 that collects the
waste heat generated within the repeater module and reduces the
thermal resistance .THETA..sub.H-M from the HOT PARTS to the
repeater MODULE. In addition, the collection member may perform, in
full or in part, the mechanical functions performed by the chassis
in known repeater housings.
Taking into account only the thermal and mechanical functions,
thermal collection member 104 is preferred over member 102 because
it fully surrounds the repeater module and thus collects waste heat
from each of its major surfaces. However, space and weight
considerations, lower waste heat transfer requirements or the fact
that a particular module generates a vast majority of its waste
heat on a single surface may favor collection member 102. In either
case, it would be ideal if the collection member's inner surface
110 and the repeater module's outer surface 112 were in intimate
mechanical contact over the full surface of the repeater module.
This would "short out" thermal resistance .THETA..sub.M-C from the
MODULE to the CHASSIS. However, mechanical tolerances and small
variations in the actual outer dimensions of repeater modules from
different manufacturers make full intimate mechanical contact
difficult and not cost effective to achieve. However, the actual
benefits from full contact in contrast to small air interfaces are
small.
For example, as in FIG. 8c, if a uniform air gap of 0.020 inches
(enlarged for clarity) was maintained between the collection member
and the repeater module, the thermal resistance .THETA..sub.M-C
from the MODULE to the CHASSIS would be approximately 0.68.degree.
C. per watt for a 239 double wide module. For an HDSL repeater
generating 6 watts of waste heat, if all that heat was transferred
across air interface 114, the differential temperature across the
interface would only be approximately 4.1.degree. C., an acceptable
fraction of the overall thermal transfer budget and a major
improvement over the prior art. If an unacceptably large air gap
were encountered, a conductive shim 116 as illustrated in FIG. 8c
could be used to replace some of the air in the thermal
interface.
The collection member also functions to reduce thermal resistance
.THETA..sub.H-M from the HOT PARTS to the repeater MODULE casing.
Repeater module casings are generally made from thin plastic or
metal and thus exhibit a relatively high thermal resistance to heat
diffusion over the surface of the casing. As a result, a hot part
will tend to produce a hot spot on the adjacent module casing that
will elevate the temperature of the hot part even if the average
temperature of the module is substantially lower. The thermally
conductive collection member acts in parallel with the module
casing's relatively high thermal diffusion resistance to bleed off
waste heat from potential hot spots.
A thermal transfer member 118, manufactured from a thermally
conductive material such as aluminum or thermally conductive
plastic, provides a conduction path that is designed to "short out"
thermal resistance .THETA..sub.C-E from the CHASSIS to the inside
of the ENCLOSURE by changing it from a natural convection and
radiation path to one using solid conduction. Analysis and tests
demonstrate that use of a transfer member 0.2 inches thick, 2
inches long and 6 inches high produces a thermal resistance
.THETA..sub.C-E of approximately 0.42.degree. C. per watt. For an
HDSL repeater generating 6 watts of waste heat, if all that heat
was transferred along transfer member 118, the differential
temperature would only be about 2.5.degree. C., a major improvement
over the thermal resistance that can be achieved with natural
convection and radiation. The thermal resistance .THETA..sub.C-E
can be further reduced and the temperature difference across the
transfer member made to approach zero by moving the repeater closer
to the side of the enclosure.
Oftentimes the transfer of waste heat to the enclosure requires
transferring waste heat across mechanical joints. The thermal
resistance caused by such mechanical joints is reduced by
minimizing the thickness of the air film sandwiched in the joint
and increasing the thermal interface area. The overlapping and
interdigitated joints 120 and 122 shown in FIGS. 8b and 8c,
respectively, solve the problem, and are particularly useful in
transferring waste heat to the housing's top and bottom
surfaces.
Distribution addresses .THETA..sub.E-A, the path from the ENCLOSURE
to the surrounding AMBIENT AIR. The largest fraction of
.THETA..sub.E-A is determined by the exposed surface area of the
enclosure that carries significant amounts of waste heat. The
larger the surface area the lower the resistance. In known
convection based repeater housings, a disproportionate share of the
waste heat is distributed to the top surface of the enclosure,
which represents only a small fraction of the available surface
area. Furthermore, the top surface is typically a horizontal
surface, which is less effective for natural convection than
vertical surfaces of equal size. Third, the thin stainless steel or
plastic enclosures are extremely poor at diffusing heat over their
surfaces and thus tend to localize the waste heat. Lastly, the
available external surface area is limited by the smooth shape of
the enclosure. Taken together, these limitations provide an
insufficient effective surface area for efficiently transferring
waste heat to the AMBIENT AIR.
The distribution members shown in FIGS. 8a-8e overcome each of
these limitations and realize a substantial reduction in thermal
resistance .THETA..sub.E-A by increasing the total surface area
that carries significant amounts of waste heat. Waste heat is
primarily distributed over the sidewalls of the enclosure, which
typically have a much larger surface area than the top and are
usually oriented in a vertical direction. Secondarily, waste heat
can also be distributed to the base and top cover. Most
importantly, the distribution member creates a thermal interface
that directly distributes the waste heat over the enclosure's
surface area rather than relying on the enclosure itself to
distribute heat. Lastly, the enclosure's external surface area can
be expanded by a factor of 200% to 400% or even more.
As illustrated in FIG. 8a, a distribution member 124, manufactured
from a thermally conductive material such as aluminum or thermally
conductive plastic, is placed in close, conformal thermal proximity
to the inner wall 126 of the environmental enclosure 128. Although
distribution elements of the invention can and will be used to
enhance thermal transfer from many different surfaces of various
types of repeater housings, in the example of the SPC 7000 series,
an aluminum distribution element averaging 0.15 thick, can turn the
vertical sides of the environmental enclosure dome into a very
effective thermal interface to the surrounding ambient air and
substantially reduce thermal resistance .THETA..sub.E-A. This
simple distribution member creates a thermal interface 129 between
the distribution member and the enclosure that directly distributes
waste heat over an enlarged vertical surface area.
As illustrated in FIGS. 8b-8e, the available external surface area
can be greatly expanded with supporting distribution. Merely
expanding the external surface area without supporting distribution
is of limited value. As shown in FIG. 8b, the environmental
enclosure, which is generally smooth sided in known repeater
housings, can be corrugated 130 to increase its surface area by a
factor of 200% to 400%. Because thin material environmental
enclosures are poor heat distributors, distribution member 124 is
shaped to contact flanks 132 of corrugations 130. As a further
refinement, distribution member 124 is formed with at least one
bifurcated distribution fin 134. This bifurcated design saves
weight and provides some slight flexibility to conform to and apply
pressure to flanks 132 of corrugations 130. For similar reasons, it
is recommended that unsupported space be left in the outer diameter
136 and inner diameter 138 of corrugations 130. In addition to
accommodating manufacturing tolerances, this flexible fin design
can also provide some cushioning to shocks from both handling and
vandalism. In a variation of this design, the environmental
enclosure might be formed from molded plastic or fiberglass over a
solid thermally conducting inner structure (not shown).
As shown in FIG. 8c, an alternate approach uses a corrugated
environmental shell 140 which is lined with a thermally conducting
material 142 to provide thermal distribution. Thermal lining 142 is
joined to the inner distribution element 124 in a thermally
conductive joint 144 using dip braising, thermally conductive
adhesives, etc. This approach allows very effective distribution to
be accomplished at minimum weight.
Yet another alternative is illustrated in FIG. 8d, in which fins
146, formed from a suitable thermally conducting material such as
aluminum, are placed on the exterior of the environmental enclosure
128. With this alternative, the primary distribution member 148 is
placed on the outside of environmental enclosure 128 and a
overlapping thermal joint 130 is used to make the thermal
connection from transfer member 118 to distribution member 148. So
long as care is taken to create a good thermal joint at the
transfer to distribution interfaces, there is little thermal
detriment to locating some or all of the distribution element on
the exterior of the environmental enclosure. Because this
alternative places thermally conductive material on the outside of
the environmental enclosure, it would only be suitable in
non-corrosive environments or if implemented with corrosion
resistant material.
The above expanded external surface alternatives are meant to
illustrate methods to maximize distribution. Many repeater housings
will not require maximum distribution. For example, FIG. 8e
illustrates a relatively simple way to expand the external surface
area of the environmental enclosure. Short fins 150 can be fastened
to the environmental enclosure 128 by a process such as spot
welding. Although the poor thermal conductivity of stainless steel
and the thermal resistance of the enclosure-to-fin interface 152
will limit the efficiency of such a design and will limit the
useful height of the fins, it is practical to double the effective
external surface area of a selected zone on a repeater housing in
this manner.
By employing the collection, transfer, and distribution principles
via solid thermal conduction, the convection based model shown in
FIG. 7 can be further simplified to a conduction based model 154 as
shown in FIG. 9. The thermal resistance from the HOT PARTS to the
MODULE .THETA..sub.H-M is primarily set by the repeater's design,
however, as discussed previously, the collection member reduces
this resistance somewhat by diffusing module casing hot spots. The
thermal resistance .THETA..sub.M-E from the MODULE to the inside
surface of the environmental ENCLOSURE is so significantly reduced
that the parallel convective paths can be eliminated from the
model. They still remain and a prudent designer will seek to
minimize them, however the effect is at most second order. Tests
have shown that .THETA..sub.M-E can be reduced to approximately
1.degree. C. per watt for a 239 double wide module, resulting in
the transfer of up to 6 watts of heat from an HDSL repeater with a
temperature differential of only 6.degree. C. The thermal
resistance .THETA..sub.E-A from the ENCLOSURE to AMBIENT AIR has
also been significantly reduced by combining the distribution
techniques with an expanded external surface area. The bottom line
is that repeater housings that could accommodate 2 or maybe 3 239
double wide modules can now accept 8-12 modules. Furthermore, these
principles can be used to design repeater housings that satisfy
both the environmental and thermal demands.
To illustrate the collection, transfer and distribution functions
and how they simplify and greatly reduce the thermal resistance,
each function was depicted in FIGS. 8a-8e as a separate physical
element. While appropriate in some applications, the separation of
elements is not always necessary of even desirable. As shown in
FIG. 10, the three functions can be integrated into a thermal
sleeve 170 formed from a single piece of aluminum extrusion. This
specific sleeve was designed for use in the repeater housing
detailed in FIGS. 12-16, and thus includes shoulder screws 240 and
an inner T-slot 268a for mounting the thermal sleeve.
Thermal sleeve 170 has an inner dimension 172 that forms a thermal
interface around repeater module 108 for collecting waste heat. The
sleeve is moved from the center of the repeater housing to the side
wall of the environmental enclosure to shorten the thermal transfer
path to the thickness of the sleeve's front surface 174. That same
front surface defines a distribution member 176 that is formed in
intimate complementary thermal contact with the enclosure side
wall's interior surface. In this case, the distribution member has
an arcuate shape that matches that of a cylindrical environmental
enclosure. The thermal sleeve is a very efficient, low thermal
resistance design that effectively "shorts out" thermal resistance
.THETA..sub.M-E from the MODULE to the ENCLOSURE and substantially
reduces thermal resistance .THETA..sub.E-A from the ENCLOSURE to
the AMBIENT AIR. Furthermore, the thermal sleeve is relatively
light weight, compact and provides the mechanical support functions
for the repeater module.
As will be described in great detail in FIGS. 12-16, the SPC 7000
Series enclosure can be modified to incorporate the collection,
transfer and distribution elements of the invention using a
plurality of the thermal sleeves shown in FIG. 10. The modified
enclosure still requires the lineman to remove the entire dome to
access the repeater modules and then tip the thermal core to access
the voltage surge protectors. In addition to the awkwardness of
this process, it requires that the dome and the distribution
members be separable, which is sub-optimal from a thermal transfer
perspective.
As will be illustrated in detail in FIGS. 19-24, the preferred
approach is to manufacture the repeater housing so that the
environmental enclosure and thermal transfer chassis are
non-separable by, for example, compression fitting or molding the
two parts together. To provide access to the repeater modules, a
seam is provided at the top of the enclosure so that a cover can be
removed, without disturbing the thermal transfer path from the
thermal chassis to the enclosure's sidewalls, to provide top/front
access to the repeater modules. In addition, the voltage surge
protector assemblies are redesigned as shown in FIGS. 11a-11d so
that the voltage surge protectors can be accessed through the top,
either independently of the repeater module or after first removing
the module.
A preferred embodiment of protector assembly 180 is illustrated in
FIG. 11a, in which the female pin portion 182 of a protector
connector is installed on a printed circuit board 184 adjacent to a
repeater connector 186. Although shown separately, these two
connectors may be merged into a single custom connector. The
individual protector elements 188 are mounted on a specially
designed printed circuit board 190 with the male pin portion 192 of
the protector connector. Alternately, the connector's male pins can
be attached directly to the protector elements thereby eliminating
PCB 190. The resulting protector assembly 180 is preferably made as
tall or taller than the adjacent repeater 108 with a slot 194 to
facilitate easy access without having to remove the repeater module
or risk contacting the high voltage present on the repeater and
protector connectors.
Because of the large and rapidly rising currents produced by
lighting or utility power cross induced voltage surges, the method
used to connect elements 188 to the repeater housing wiring is
critical. First, the telecom wires should be routed to the female
protector connector 182, not to repeater connector 186. Second, the
protector connector must be designed with sufficient spacing
between individual contacts to resist high voltage breakdown and
utilize contact elements capable of carrying the high currents
expected. Third, the interconnection between the male protector
connector 192 and the individual protector elements 188 must be
capable of carrying these high currents and have a low inductance
that passes the rapidly rising current waveform with minimum
impedance. A multi-layer printed circuit board with heavy and wide
copper traces, designed with very high speed circuit layout
practices, can meet these requirements.
Another advantage of this type of protector assembly is that it can
easily accommodate test jacks 196 and/or indicator lights 198, as
illustrated in FIG. 11b, that are able to take advantage of
electrical access to the repeater wiring and combine it with direct
top/front access. If desired, the individual protector elements can
either be permanently connected to PCB 190 or can be installed in
sockets to allow individual service. As illustrated in FIG. 11c,
the assembly can also accommodate non-cylindrical protector
elements 200 such as solid state voltage surge protectors.
An alternative protector assembly 202 is illustrated in FIG. 11d,
in which protector access without repeater removal is sacrificed
for a smaller footprint. The female repeater connector 204 is
elevated so that the female protector connector 206 is installed
under the repeater module. The protector elements are mounted on a
PCB with an edge connector 208 that is inserted into connector 206.
PCB edge connector 208 is used for illustration only in that a
connector style with higher current ratings might be required for
this application. This alternate embodiment still provides direct
access to the protectors from the top or front of the repeater
housing, safe access without the use of special tools and the
ability to accommodate a wide range of protector elements.
The repeater housing 210 illustrated in FIGS. 12-16 is a modified
SPC Series 7000 repeater housing that incorporates the collection,
transfer and distribution techniques described in FIGS. 8-10 above
with the existing thin-walled stainless steel environmental
enclosure. By using the existing Series 7000 to provide the
environmental enclosure wiring, connectors, telecom accessories,
pressurization and vent fittings, sealed mechanical joints, deep
drawn, stainless steel thin wall environmental enclosures, etc.
necessary to a repeater housing, Applicant avoided the need to
develop, test and gain telecommunications industry approval for
these elements, which are necessary in a repeater housing, but
incidental to the thermal problem.
As shown in FIGS. 15a-b, the environmental enclosure of housing 210
includes a base 212 and a dome 214 that are fabricated as seamless
thin, approximately 0.035 inch thick, deep drawn stainless steel
cylinders having flanges 216 and 218 formed at their respective
open ends. An O-ring 220 is positioned on flange 218 and secured in
position by O-ring support 222. When dome 214 is installed, the
inside wall of the dome fits snugly over O-ring support 222 with
its flange 216 resting on O-ring 220. A V-groove clamp 224 is drawn
tight over the O-ring assembly to mechanically fasten base 212 and
dome 214 together and seal their joint.
A stainless steel mounting bracket 226 is fastened to the bottom of
base 212 using threaded studs 228 (only 2 of which are shown) which
are welded to base 212. A cable stub 230 is inserted through into
base 212 using a fitting 232 designed to provide both strain relief
for the cable stub and sealing of this entry. Not shown are
additional fittings, such as pressurization, venting and
telecommunications accessories that pierce the bottom surface of
base 212. These additional fittings are each designed with features
to seal their entry points into the base 212. For additional
sealing integrity, the bottom of the base and the various fittings
that pierce the base are covered with a semi-rigid encapsulant
234.
A plurality of thermal sleeves 170 are positioned inside dome 214
to form a cylindrical thermal core that is in complementary thermal
contact with the inner surface of dome 214. Because HDSL repeaters
have a high thermal density that is distributed throughout the
module, the 4-surface collection provided by the sleeve is
desirable. Furthermore, by moving the sleeve to the periphery of
the thermal core, the transfer member can be reduced to the
thickness of the sleeve, virtually shorting out the thermal
resistance to the enclosure. Based upon the amount of waste heat
generated by the HDSL repeaters, the maximum specified ambient
temperature, the amount of waste heat that can be transferred to
the ambient air through the top of the dome and the base and
assuming a below ground environment, each sleeve's distribution
member 176 was required to be approximately 10 inches high and
occupy approximately 45 degrees of the circumference of the dome to
provide a large enough thermal interface to accommodate 8 HDSL
repeater modules.
In order to service the repeater housing, a lineman must be able to
remove dome 214. However, to maximize thermal transfer to the
ambient air the sleeve's distribution members should be held in
close if not intimate thermal contact with the dome. To this end,
an actuator mechanism 236 urges the sleeves against the dome's
sidewalls when it is sealed to the base and retracts the sleeves to
allow the dome to be removed. From the thermal transfer standpoint,
alternatives considered included 1) spacing the sleeves away from
the dome at a distance sufficient to accommodate manufacturing
tolerances and allow easy installation and removal of the dome or
2) spring loading the sleeves against the inside of the dome
surface with a force light enough to allow the cover dome to be
conveniently installed and removed. One of the environmental
conditions for which repeater housings must be designed is what the
telecommunications industry refers to as a Zone 4 earthquake. Mere
spring loading probably would not provide enough support to protect
the electronics inside the dome.
In order for actuator mechanism 236 to move sleeves 170 radially,
each sleeve is secured to a platform 238 with four shoulder screws
240 (FIG. 13) positioned in slots 242 (FIG. 14) so as to guide but
restrain sleeves 170. Since repeater modules 108 must move with the
sleeves, repeater connectors 244 (FIG. 13) must be free to move in
concert with the sleeves. Therefore, as illustrated in FIGS. 12 and
13, a connector clip 246 is secured to repeater connector 244. The
clip's ears 248 spring outward about 10 degrees and fit into
alcoves 250 (FIG. 14) formed into the sleeves thereby aligning each
repeater connector with its host sleeve and forcing each repeater
connector to move radially in concert with its host sleeve. To
restrain repeater connectors 244 in the vertical direction, they
are positioned in cut-outs 252 (FIG. 14) in platform 238 while
mounting connector ears 254 on the connector rest on the platform
and stops 256 on the connector clip slide under the platform. A
standard SPC voltage surge protector assembly 258 is plugged on to
the connector's wire wrap pins 260 and can, therefore, move with
the sleeve. Repeater retainer 262 is used to secure a repeater
module once plugged into a sleeve assembly.
Platform 238 and an assortment of sleeve positions are illustrated
in FIG. 14. Starting at 12 o'clock and working in a
counterclockwise direction as indicated on mast cap 241, position
number 1 shows the shoulder screw slots 242 and repeater connector
cut-out 252 in platform 238. Position 2 shows an installed 239
mini-repeater, which is held in position with guides 262 mounted in
guide slots 264 formed in the sleeve's extruded wall. Positions 3
and 7 show sleeves and their repeater connectors. Positions 4, 6
and 8 are shown with 239 Double Wide repeater modules installed.
Position 5 shows a sleeve with neither repeater connector nor
repeater installed. The sleeves in positions 2,3 and 4 are shown
expanded against dome 214. The sleeves in positions 6, 7 and 8 are
shown in the fully retracted position, a travel distance of
approximately 0.1 inches.
To move the sleeves radially and exert the pressure necessary to
hold them against the inside surface of the cover dome in the
presence of worst case earthquake forces, actuator mechanism 236 as
shown in FIG. 13 includes a modified parallelogram spring 266 that
translates the vertical motion of a mast assembly 267 into radial
force for retraction and expansion of the sleeves. Each
parallelogram spring 266 slides into complementary T-slots 268a and
268b (shown best on FIG. 10) formed in each sleeve and on the eight
faces of mast hub 270. Once installed, the parallelogram spring is
retained in position on the glove by a Hamm latch 272 and on the
mast hub by a bottom mast cap 274 and a top mast cap 276.
As shown best on FIGS. 15A and 15B, a mast shaft 278 passes through
mast hub 270 and through a hole in platform 238. The upward travel
of the mast shaft is limited by an E-clip 280. The upward travel of
the mast hub with respect to the mast shaft is limited by an
assembly of thrust bearings 282 and another E-clip, thus allowing
the mast shaft to rotate within the mast hub. Mast hub 270 is urged
upward by a spring 284, which has sufficient strength to retract
all eight gloves against the worst case combination of tolerances,
wear and friction expected over the repeater housing's operating
life.
In order to expand the sleeves, top drive screw 286 is screwed down
into its mating top drive seat 288. As the top drive screw moves
downward, the attached alignment cone 290 engages the top of mast
shaft 278 (the length of which can be adjusted in manufacturing to
offset tolerance buildup). As the top drive screw continues
downward, thrust bearings 282 allow mast shaft 278, which is now in
frictional contact through the alignment cone 290 with top drive
screw 286, to freely rotate within mast hub 270. The downward
motion of the top drive screw now forces the mast shaft and mast
hub downward until the top drive screw reaches the end of its
travel against the top drive seat. The top drive assembly contains
o-ring seals and sealing surfaces sufficient to prevent leakage
into or from the environmental enclosure once the top drive screw
is seated against the top drive seat.
As top drive screw 286 forces mast shaft 278 and mast hub 270
downward, toward platform 238, the portion of each parallelogram
spring 266 fastened to the mast hub must also move toward the
platform. Since the other side of the parallelogram spring is
fastened to sleeve 170 and the sleeve is fastened to the platform,
the only degree of freedom allowed the parallelogram spring is to
force the sleeve radially outward, away from the mast. As
illustrated in FIGS. 15a and 15b, which respectively show the
actuator mechanism in its expanded and retracted positions, the
arms of the parallelogram spring not fastened to the mast hub or
sleeve are designed to flex in order to accommodate the range of
motion needed from the mast hub to provide for adequate expansion
and retraction forces over the full range manufacturing
tolerances.
In addition to the thermal transfer through the sleeve's
distribution member to the sidewalls, FIGS. 15a and 15b also
illustrate another important waste heat transfer and distribution
path. Sleeves 170 rest upon platform 238 and, therefore, although
this is a poor quality thermal joint, can transfer some heat to the
platform, which is manufactured from aluminum thicker than required
for its structural purpose. Thick aluminum bars called downrights
292 are welded to the platform to form a good thermal joint, which
are, in turn, attached to an aluminum frame called uprights 294 at
two pivot points 296 using overlapping thermal joints 298. The
pivot points allow the thermally enhanced chassis, which is
everything attached to the platform, to tilt as illustrated in FIG.
16 for access to the underside of the platform and, in particular,
to the voltage surge protector modules 258.
The upright bracket is bent to form a large foot 300 that is
secured to base 212 with welded studs 302. Although the base is
thin stainless steel of poor thermal conductivity, this design
creates an overlapping thermal joint by placing the feet of the
upright brackets in close proximity with flanges 304 by which the
repeater housing mounting bracket 226 is secured to the repeater
housing base. This is not a primary thermal transfer and
distribution path, however, the effort and cost required to create
it are relatively small and the heat removed via this path can
reduce the temperature of the rest of the repeater housing and the
installed repeaters several degrees centigrade.
Similarly, although natural convection within the repeater housing
is no longer the primary heat transfer method, it is prudent to
continue to utilize all available thermal transfer paths.
Therefore, as shown most clearly in FIG. 14, numerous air holes 306
are placed in the platform to facilitate the circulation of air
from the base to the top of the cover dome and small corrugations
308 are formed on the outer surfaces of the sleeves to slightly
increase the surface area and substantially increase the radiation
emissivity.
In addition to the waste heat generated within the repeater
housings, solar loading, i.e., the heat absorbed from solar energy
incident upon above ground repeater housings, can be a serious
problem. The SPC 7000 Series enclosure may intercept up to 150
watts of incident energy. With an appropriate white coating and
allowing for aging and normal surface contamination, it is
practical to attain 70% reflectance from a smooth surface repeater
housing. However, up to 45 watts of solar energy may be absorbed,
which is equivalent to over 7 HDSL repeaters.
One solution is to expand the surface area of the repeater housing
a sufficient amount to transfer the additional solar energy to the
surrounding ambient air. If the expanded area is achieved with fins
or convolutions of the surface, the area can be increased
substantially with a minimal increase in the projected area of the
housing that captures the solar energy. Unfortunately, this
prospective solution is also limited in that such fins or
convolutions also significantly reduce the surface reflectivity.
This occurs because such fins and convolutions cause multiple
reflections and, thereby, become light traps. Fins or convolutions
sized to double the effective surface area of a repeater housing
would also reduce the reflectivity of a 70% reflective surface to
40% or less on the expanded surface area. This problem is overcome
by placing a reflective solar shield around the expanded surface
area.
The solar shield assembly 350 illustrated in FIG. 17 includes
stainless steel fins 352 that are spot welded to the sidewalls of
dome 214 and a thin stainless steel cylinder 354 is spot welded to
fins 352 to form an annular ring spaced about 1.25 inches from dome
214, with the entire assembly then painted with an appropriate
white coating. A debris skirt 356 is fastened to the environmental
enclosure above seam 358 with base 212 to prevent debris from being
caught on the edge of V-groove clamp 224.
Solar shield assembly 350 functions as follows: when the sun angle
is high overhead, little solar energy is incident upon the vertical
sides of the repeater housing. The smooth white cover reflects a
large fraction of the incident solar energy and the inner portions
of the fins closest to the environmental enclosure increase the
external surface area sufficiently to dissipate the extra solar
energy to the surrounding ambient air. Although thin stainless
steel fins are poor thermal conductors, as previously explained and
illustrated as FIG. 8e, short fins can be useful.
As the sun angle shifts from the vertical towards the horizontal,
the solar shield 354 intercepts most of the solar energy that would
otherwise heat the vertical side of the environmental enclosure
dome 214. This, of course, heats the solar shield. However, the
shield has both its inner and outer surfaces available to transfer
the solar energy into the surrounding ambient air via natural
convection. Furthermore, the outer portions of fins 352 also serve
as an expanded external surface to aid in the natural convection
transfer. This combination of surfaces is more than enough to
dissipate to the ambient air the solar energy absorbed by solar
shield 354 and that portion of the fins 352 exposed to the solar
radiation.
In some applications, it is desirable for the environmental
enclosure to operate at a temperature lower than that of the solar
shield. In such cases, it is important to minimize the heat
conducted from the solar shield 354 through fins 352 to
environmental enclosure 214. FIG. 18a illustrates a portion of fin
352 having an inside tab that is fastened to the environmental
enclosure and an outside tab that is fastened to the solar shield.
If manufactured from a material of only moderate thermal
conductivity such as stainless steel, the inner and outer portions
of the fin near the environmental enclosure and the solar shield,
respectively, will serve as an extra surface from which to
dissipate heat into the natural convective air flow. However, if
designed correctly, the fin will not be effective at conducting
significant amounts of heat the full width of the fin from a hotter
solar shield to a cooler enclosure as heat is removed from the
surfaces of the fin via natural convection.
FIGS. 18b and 18c illustrate ways to use parts of fin 352 as
natural convection surfaces while increasing thermal isolation
between the environmental enclosure and solar shield 354. In FIG.
18b, slots 360 have been cut in the fin to reduce the cross
sectional area available for thermal conduction while leaving
enough material to maintain mechanical integrity. In FIG. 18c, in
addition to the slots, the conductive distance has been increased
by adding a series of bends 362 to the portion of the fin providing
the mechanical connection.
Although the modified SPC 7000 Series repeater housing illustrated
in FIGS. 12-16 incorporating the solid thermal conduction
collection, transfer and distribution principles represents a
substantial improvement in thermal transfer capability over the
known SPC 7000 Series, it still suffers from the access
difficulties associated with "tilt, swivel and around the back" and
requires a moderately complex mechanism to expand and retract the
thermal sleeves, accommodate an accumulation of manufacturing
tolerances, wear and tear, survive a zone 4 earthquake and protect
its housed repeaters from a shotgun blast at close range. These
limitations are overcome by,incorporating the thermal transfer
techniques described in FIGS. 8a-8e, 9 and 10 with the voltage
protector assemblies described in FIGS. 11a-11d that facilitate
direct top or front access.
Although applicable to any housing shape or configuration, the
technique is illustrated in the context of two different
cylindrical repeater housings. The first, illustrated in FIGS. 19
and 20, is designed for use above-ground in a vertical orientation.
The second, illustrated in FIGS. 21-24, is designed for use
below-ground in a horizontal orientation. The intended orientation
is important because it dictates the orientation of the external
fins to optimize natural convective air flow.
As shown in FIGS. 19 and 20, an above-ground cylindrical repeater
housing 400 comprises a cylindrical base 402 that receives a cable
stub 404 that is preferably terminated with a master connector 406.
A mounting bracket 408 is used to mount the base 402 in an upright
position on a telephone pole, for example. A plurality of repeater
connectors 410 are disposed radially around a PCB 412 with their
protector connectors 414 positioned towards the center of the PCB.
A mating master connector 416 is positioned at the center of the
PCB for connection to master connector 406. Alternately, any of the
protector assemblies illustrated in FIGS. 11a-11d could be used and
the connectors could be wired using conventional wire-wrapping
techniques instead of the master connector. Furthermore, if on-site
access to the wiring is not required, the base can be eliminated
and the cable and connections below the PCB encapsulated to provide
the necessary mechanical strength and environmental protection at a
considerable cost savings.
A thermal chassis 418 is placed over PCB 412 to define a radial
slot 420 over each repeater connector 410 and provides the
collection, transfer and distribution functions as described in
detail previously, and, preferably, to define an inner slot 422
over each protector connector 414. Repeater modules 424 and
protectors 426 are inserted in slots 420 and 422, respectively, and
mounted in connectors 410 and 414. The outer surface of thermal
chassis 418 is preferably formed with an axial extrusion pattern
428 such as the bifurcated fins 430.
A thin-walled shell 432, manufactured from a material suitable for
environmental protection such as stainless steel, plastic or
fiberglass, fits in complementary thermal contact around thermal
chassis 418. Shell 432 is preferably corrugated to define a
plurality of axial fins 434 that fit over the chassis' extrusion
pattern 428. Alternately, shell 432 and chassis 418 could utilize
any of the other expanded external surface designs illustrated in
FIGS. 8a-8e or even a smooth sided, non-expanded design.
Flanges 436 and 438 are formed at both ends of shell 432 for
connection to base 402 and an access cover 440, respectively, using
V-groove clamps and seals (not shown). The seam at flange 436
provides bottom access to the wiring on the underside of thermal
chassis 418. This is useful during manufacturing and on very rare
occasions in the field. The seam at flange 438 provides direct top
access to thermal chassis 418 for removing repeater modules 424 and
voltage surge protectors 426.
Thermal chassis 418 and thin-walled shell 432 can be manufactured
in many different ways depending upon the requirements of a
specific repeater housing such as thermal transfer capacity,
quantity and type of repeaters and cost. One approach is to use a
thermally conductive adhesive to glue together a plurality of
thermal sleeves 442, similar to the one shown in FIG. 10 but
extended to cover the protector connector and rotated ninety
degrees to optimize the available space. Extrusion pattern 428 can
be either formed into the distribution surface of the sleeve or
separately fastened thereto. Alternately, the entire thermal
chassis 418 can be cast or molded as a single unit or molded inside
the shell 432. In addition, individual thermal sleeves could be fit
inside the shell and mechanically secured so that they could be
disassembled at a later time.
Shell 432 can be a separate piece, formed, cast or molded with the
desired complementary extrusion pattern, that is slid over the
thermal chassis to provide a compression fit. The compression fit
can be improved by forming the chassis and shell with a
complementary taper as shown in FIG. 19 that forces the chassis'
extrusion pattern into the shell to provide a good thermal and
mechanical joint. Alternately, the shell can be molded over the
chassis using a moldable material such as plastic. This approach
avoids the need for a tapered design and accommodates the
manufacturing tolerances of the chassis in the wall thickness of
the shell.
Because repeater housing 400 is intended for use above ground, it
should also accommodate solar loading. One approach is to place a
solar shield of the type illustrated in FIG. 18 around the housing.
In addition, thermal transfer from access cover 440 to the chassis
should be minimized. This is accomplished by making the joint
between the cover and chassis a poor thermal conductor and possibly
insulating the inside of the access cover. In contrast, thermal
transfer from the chassis to the relatively cool base 402 and to
mounting bracket 408 should be encouraged. This is accomplished
using a combination of overlapping and interdigitated thermal
joints not illustrated for this embodiment, but using the
techniques described for the front access cover in the horizontal
cylinder ahead. In addition, thermal sleeves 442 and particularly
the portion that defines the inner slot for the protectors are
designed to form overlapping thermal joints 444 that form a
cross-conduction path around the interior of the chassis. As a
result, heat from a sunny side of the housing can be transferred to
the shady side through the cross-conduction path.
As shown in FIGS. 21 through 23, below-ground cylindrical repeater
housing 500 is similar to the above ground version except that a)
the fin structure is formed circumferentially around the enclosure,
rather than axially, to conform to the fact that hot air rises and
that b) solar loading is not a concern. As shown, the thermal
chassis' extrusion pattern includes a plurality of circumferential
corrugations, or fins, 502 that match the shell's circumferential
corrugations 504. With a circumferential fin/corrugation pattern,
the shell cannot be slipped over the thermal chassis. While it is
possible to insert individual thermal sleeves into the shell, some
volume and distribution efficiency would be lost. More appealing
are the two alternatives of either molding the shell over the
chassis or molding the chassis inside the shell. As shown, the
shell 506 can be molded over chassis 508.
For this horizontal embodiment, an additional manufacturing
alternative is illustrated in FIG. 24, in which the circumferential
corrugations 504 are inclined from the axis of the cylinder to form
threads and the fins 502 on the chassis are similarly inclined.
With these matched threads, a chassis and an outer shell can be
mated by screwing them together. If the chassis and shell are also
tapered, the threaded and tapered components can be assembled in a
manner and with the benefits discussed for the tapered vertical
cylinder embodiment.
The absence of solar loading underground provides an opportunity to
use expanded surfaces on both ends of the repeater housing. As
illustrated in FIG. 21, a thermal interface member 520, formed from
a suitable thermally conductive material such as aluminum or
thermally conductive plastic, transfers waste heat from the chassis
to the front access cover 522. The exterior of interface member 520
has fins 524 that fit within corrugations 526 formed in access
cover 522. The interior surface of interface member 520,
illustrated in plan view in FIG. 22b, has formed on it triangularly
shaped thermal conductors 528 that fit within mating triangular
slots 530, illustrated in FIG. 22a, in the thermal chassis and
implements twelve sets of overlapping thermal joints to transfer
waste heat from the chassis to the access cover. Similarly, a
twelve faced ring 523 is formed about the center of interface
member 520 to form an additional thermal interface joint with the
interior twelve sided surface formed by the juncture 534 of the
individual thermal sleeves that combine to form the chassis.
The side profile of these overlapping thermal joints is illustrated
in FIG. 23a where the access cover is removed in FIG. 23b where the
access cover is in place. For purposes of clarity, the base is
shown in a side, rather than a sectional view, but would
incorporate a similar interface structure for transferring heat to
the mounting bracket. Although this interface member is used in
this embodiment to transfer heat to the front access cover, similar
interface members, utilizing overlapping and/or interdigitated
thermal transfer joints, can be used to move heat to other regions
within and without repeater housings, certainly including to the
repeater housing base as anticipated in the preceding discussion of
the vertical cylinder embodiment.
While several illustrative embodiments of the invention have been
shown and described, numerous variations and alternate embodiments
will occur to those skilled in the art. For example, although the
invention was discussed in the context of the cylindrical SPC 7000
type enclosure, the principles are equally applicable to other
housing shapes, rectangular, for example. Although repeater
housings for 8 and 12 239 mini and double wide repeaters have been
illustrated, the invention can be applied to repeater housings
intended for greater and smaller repeater quantities and for other
repeater types such as the type 400. Although the direct access
voltage surge protector design has been shown in association with
the thermal elements of the invention, such direct access protector
designs are expected to find application in repeater housings where
thermal enhancement is not required, but improved access could be
of value. Such variations and alternate embodiments are
contemplated, and can be made without departing from the spirit and
scope of the invention as defined in the appended claims.
* * * * *